1. Field of the Invention
The present invention pertains to a fluid filled vibration damping device that exhibits vibration damping effect on the basis of flow action of a non-compressible fluid sealed therein, and in particular relates to a fluid filled vibration damping device suitable for use in an automotive engine mount, body mount, or cab mount, for example.
2. Description of the Related Art
There have been widely used in a variety of fields vibration damping devices each having a rubber elastic body disposed between first and second mounting members fixable to components connected together in vibration isolating fashion. As one type of such vibration damping devices, there is known a fluid filled vibration damping device in which the rubber elastic body partially defines a fluid chambers filled with a non-compressible fluid sealed therein. JP-A-2002-81491 and JP-B-3-30736 disclose examples of such a fluid-filled vibration damping devices.
The fluid-filled vibration damping device of this construction is capable of exhibiting vibration damping effect on the basis of resonance or other flow actions of the non-compressible fluid created within the fluid chamber in association with elastic deformation of the rubber elastic body during input of vibration, thereby readily affording low dynamic spring action and high attenuating action in the tuning frequency range at levels not achieved simply by damping action of a rubber elastic body. For this advantage, the fluid-filled vibration-damping device has been studied to apply to automotive vibration damping devices in which high levels of damping performance are required in certain specific frequency ranges.
Extensive researches conducted by the inventors has revealed that the fluid filled vibration damping devices of conventional design may possibly suffer from deterioration in the damping performance, when a relatively large load is input to the rubber elastic body in the opposite direction (rebound direction) from the direction in which initial load is exerted (bound direction) due to the distributed support load of a power unit, that is, in the direction that expands the volume of the fluid chamber.
Namely, in the conventional fluid-filled vibration damping device, is sealed a non-compressible fluid within the fluid chamber whose wall is partially defined by the rubber elastic body. Therefore, when a relatively large load is input in the opposite direction from the direction in which initial load is exerted on the rubber elastic body, the sealed fluid undesirably exerts constraining force on the rubber elastic body in a direction tending to inhibit elastic deformation of the elastic body. This creates a rubber elastic body dynamic spring constant that is greater than that of a rubber elastic body alone, resulting in deterioration in damping performance.
In the case of a mounted type fluid-filled vibration damping device of a design wherein negative pressure is generated within the fluid chamber in the event of a large load input in opposition to the rebound direction, there are a risk that the resultant large negative pressure created within the fluid chamber will result in separation and bubble formation of air component contained in the sealed fluid, and a risk of problems with noise and shock as bubbles form and disappear. Further, air bubbles formed within the fluid chamber due to separation of air component present in the fluid can also undergo compression during vibration input, leading to insufficient increase in the interior pressure of the fluid chamber. As a result, there is likelihood that the mounted-type fluid-filled vibration-damping device fails to provide a desired level of damping performance during vibration input.